Modern surgical procedures often necessitate localized diagnosis, or treatments applied to relatively inaccessible interior areas of the body. In the past, such procedures have typically involved invasive surgery, enabling the physician to visually identify or treat the area of interest by accessing a relatively large opening or incision made in the body. Unfortunately, invasive surgical methods often include undesirable side-effects, from the tissue trauma associated with the procedure. Often, the effects of the trauma prolong the healing and rehabilitation period for the patient.
To minimize the trauma often associated with invasive surgery, those skilled in the art have developed relatively small surgical instrument, such as catheters, for insertion into the vasculature of the body. Typically, the particular surgical instrument accesses the body through a small incision made near the skin, where it can then be advanced to an area of interest. However, in order to navigate through the vasculature in a predictable manner, the instrument must be precisely controllable to position, as examples, ablation electrodes or imaging probes proximate specific tissues of interest.
To enable manipulation of the instrument, such as a catheter, inside the body, a number of mechanism may be used to selectively “steer” the distal tip of the catheter while the operator inserts the device into the body. One such mechanism is a slidable control wire mechanism which includes a pair of control wires that span the length of the catheter shaft, or body. The control wires have respective distal ends anchored to specific locations at the distal tip of the catheter body corresponding to predetermined deflectional movement. The proximal ends of the wires are mounted to a slider mechanism that responds to the operator by placing one of the wires in tension, pulling at the catheter end for deflection in a first direction, while simultaneously compressing, or buckling, the other wire. An example of such a catheter configuration incorporating such a control mechanism is found in U.S. Pat. No. 5,383,852, assigned to the assignee of the present invention, and herein incorporated by reference in its entirety.
Typically, the surgical instrument includes a handle component. Handles for deflectable tip instruments typically rely on the user to generate the force required to deflect the tip member in either direction, to maintain deflection, and to return the tip member to center after deflection. Devices which accomplish the foregoing are often referred to as having bidirectional steering. Sometimes, the tip member is only deflected in one direction and is relied upon to generate the force required to return the tip member to center. These devices are referred to as having unidirectional. In all of these conventional handle designs, the handle is a passive component. The handle does not generate any force, it merely delivers the force applied by the user.
When the distal end of the instrument body, e.g. catheter body, is deflected, a force is generated that tends to drive the distal end back to its straightened position. This is commonly referred to as a “return to center” force. This is usually not a desired effect, for in use, it is often convenient for the user if once the catheter body is deflected, it remains so without the continuing input of force from the user to counter the return to center force coming from the catheter body. Existing passive instrument designs have needed to rely on friction, ratchets, or other “drag” mechanisms for producing this counter effect. For example, one such counter mechanism uses a set screw included within the handle to hold the catheter body in various locations so as to prevent the distal end of the catheter body from straightening out when the physician releases the handle. The set screw generally applies a friction force to the operational components of the handle. The friction force applied to the handle components must, of course, be greater than the maximum force generated by the distal end of the catheter body. The maximum force is generated when the distal end is in its most curved orientation. One of the associated disadvantages of such counter mechanisms is that in order to achieve the required drag to maintain the shape of the catheter body, the force required to deflect the distal end may be inconvenient to the user. In other words, it may be difficult for many users to conveniently use a thumb or finger to manipulate the handle to cause deflection of the distal end because the force required to do so is too great.
U.S. Pat. No. 6,013,052 ('052) to Durham et al. discloses a catheter handle having a piston-type actuator device along with a biasing element which biases the piston in the distal direction. The '052 patent is hereby incorporated by reference in its entirety. The device disclosed in the '052 patent is of the type which has unidirectional steering. One of the associated disadvantages with this type of biasing mechanism is that the mechanism is only designed for use with unidirectional steering devices. In other words, the biasing mechanism counters only one direction one movement of the deflectable tip. As procedures become more complex and to permit greater latitude in performing the procedures, it is more desirable to use bidirectional devices in comparison with unidirectional devices. One of skill in the art will appreciate that it is significantly more difficult to provide an active counterforce mechanism for a device having bidirectional steering. One reason is that there is limited room in the housing to position a mechanism which can translate bidirectional movement into one direction on the control mechanism of the deflectable tip.
Therefore, those skilled in the art have recognized the need for a bidirectional mechanism to counter the return to center force generated by the deflected distal end such that the catheter body remains in a deflected state without the continuing input of force from the user while as the same time the force required to initially deflect the distal end is reasonable.